OBJECTIVES: Poor adherence to antihypertensive regimens has frequently been cited as a factor for failing to achieve blood pressure goals in patients with hypertension. The objective of our study was to determine factors associated with adherence to antihypertensive regimens in members enrolled in a commercial managed care organization (MCO). METHODS: All members evaluated had a diagnosis of hypertension and were continuously enrolled during the one-year study period. Severity of illness was stratified by co-existing medical complications associated with hypertension. Members receiving one or more antihypertensive medications were the population evaluated in our retrospective analysis. Average medication possession ratio (MPR) on all antihypertensive medications was used as the primary adherence indicator in this study. Factors evaluated included member age, gender, severity of illness, number of concurrent antihypertensive medications, dosing schedule, and sum of total days supply of medication. Variable were evaluated using a forward step-wise regression analysis. RESULTS: There were 3306 members identified with hypertension in the MCO. MPR was evaluated in 2116 members on antihypertensive medications. The mean age was 52.2 years and 47% were female. The most common classes of antihypertensive medications utilized were Calcium Channel Blockers, ACE Inhibitors, and Diuretics. The regression model for average MPR was significant (F=127.72, p<0.001). Factors significantly correlated with average MPR were total days supply (ß=0.73, p<0.001), age (ß=0.08, p<0.001), number of current medications (ß=-.057, p<0.001) and dosing schedule (ß=0.08, p<0.001). CONCLUSIONS: A number of factors were found to be significant predictors of adherence to antihypertensive medications. Members that were older and received the drugs for longer periods of time had better adherence. Adherence to medication tended to decrease as the number of concurrent medications increased and as the number of doses of medication taken per day increased. Disease severity and gender were not found to be significant predictors of adherence.